Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons

Definitions

• This invention relates to reductive dehydrohalogenation of ⁇ -haloalcohols to give alkenes, and more particularly it relates to the reductive dehydrochlorination of chloral adducts with alkenes.
• This procedure is not well suited to large scale preparation of the required diene because it involves a large number of separate steps, it uses a relatively large quantity of zinc dust which can give rise to problems of effluent disposal, and uses ether in conjunction with the zinc powder at one stage which makes that particular step potentially very hazardous because of the high flammability and low flash point of ether and the pyrophoric nature of finely powdered zinc dust.
• an improved process for the preparation of a compound of formula: ##STR1## wherein X is halogeno and R is either a group of formula: ##STR2## or a group of formula: ##STR3## comprises treating a haloalcohol of formula: ##STR4## with powdered zinc in glacial acetic acid at a temperature within the range 25° to 110° C, wherein the zinc is used in an amount of from one to two moles per mole of haloalcohol.
• the improved process is preferably conducted at a temperature within the range 40° to 60° C.
• the quantity of zinc used is preferably within the range from 1.4 to 1.6 moles of zinc per mole of haloalcohol.
• the use of zinc in the amounts specified in the invention process represents a considerable saving over the amounts proposed by Farkas et al. This saving is not only made as a result of using less zinc, which is in itself valuable, but also in the reduction of the cost involved in plant and processes to recover the spent zinc from the reaction mixture and also a reduction in the cost of providing adequate effluent control to prevent wastes contaminated with zinc or zinc salts from affecting the environment.
• the improved process of the invention also represents an advance over the known process in that the haloalcohol itself may be directly reduced without the necessity of first converting it to the acetate.
• 1,1-dihalo-4-methyl-1,3-pentadienes and 1,1-dihalo-4-methyl-1,4-pentadienes may be useful as monomeric intermediates in the preparation of copolymers with other ethylenically unsaturated monomers, for example, vinyl chloride, vinyl acetate, acrylonitrile, methyl methacrylate, and the like. They may also be useful in the preparation of resins, for example, alkyd resins.
• halo or halogeno as used herein we mean fluoro, chloro, bromo and iodo.
• 1,1-dihalo-4-methyl-1,3-pentadienes are also useful in the synthesis of certain insecticidal cyclopropane derivatives.
• 1,1-Dichloro-4-methyl-1,3-pentadiene and 1,1-dibromo-4-methyl-1,3-pentadiene are particularly useful for this purpose, and can be reacted with alkyl diazoacetates to provide the alkyl esters of 2(2,2-dichlorovinyl)-3,3-dimethylcyclopropane caraboxylic acid, and 2(2,2-dibromovinyl)-3,3-dimethylcyclopropane carboxylic acid respectively.
• Certain esters of these acids for example, the 3-phenoxybenzyl, and ⁇ -cyano-3-phenoxybenzyl esters, are extremely potent insecticides.
• these conjugated dienes may be obtained from the corresponding unconjugated 1,4-dienes, for example by heating with an organic acid.
• the invention provides a process for the preparation of a compound of formula: ##STR5## wherein X is chloro or bromo, which comprises (a) the step of treating a haloalcohol of formula: ##STR6## wherein R represents either the group of formula: ##STR7## or the group of formula: ##STR8## with powdered zinc in glacial acetic acid at a temperature within the range 25° to 110° C, wherein the zinc is used in an amount of from one to two moles per mole of haloalcohol; and (b) the additional step of subsequently heating the reaction mixture at a temperature within the range 80° to 120° C with a catalytic quantity of an organic acid (other than acetic acid), to cause isomerisation of any of the unconjugated 1,4-diene formed in the first stage to the conjugated 1,3-diene. It is particularly convenient to raise the temperature of the reaction mixture for this additional step to the reflux point.
• haloalcohols of formula: ##STR9## wherein X and R are as defined hereinable, may be obtained by a procedure analogous to that of Colonge et al (loc. cit.), from trihaloacetaldehyde and isobutylene in the presence of a Friedel-Crafts catalyst, for example aluminium chloride.
• a Friedel-Crafts catalyst for example aluminium chloride.
• the invention is illustrated by the following example.
• This example illustrates the condensation of chloral and isobutylene.
• This example illustrates the preparation of 1,1-dichloro-4-methyl-1,3-pentadiene.
• a stirred mixture of 1,1,1-trichloro-2-hydroxy-4-methyl-4-pentene (671 g) and glacial acetic acid (792 g) was heated to 50° C and powdered zinc (324 g) was added in small portions over a period of 100 minutes, the temperature of the mixture during the addition being maintained in the range 47° to 50° C. When the addition was complete the mixture was stirred at 50° C for a further 4.5 hours.
• p-Toluenesulphonic acid (4.0 g) was then added to the mixture at the temperature raised 108° C, whilst purging the mixture with nitrogen.
• the mixture was then heated under a nitrogen atomosphere within the range 105° to 108° C for 8.5 hours, following which acetic acid (ca. 160 ml) was removed from the mixture by distillation, and the residual mixture cooled to the ambient temperature, and diluted with water (900 ml) and light petroleum (boiling range 60° to 80° C, 250 ml). After vigorous stirring the phases were separated. The aqueous phase was washed with more light petroleum (3 ⁇ 250 ml) and the washings combined with the original petroleum phase. The combined petroleum phase was washed with saturated aqueous sodium bicarbonate solution (2 ⁇ 250 ml), and with water (1 ⁇ 250 ml), and finally dried over anhydrous magnesium sulphate.
• acetic acid ca. 160 ml
• the solvent was removed by evaporation under reduced pressure and the residual oil distilled yielding 1,1-dichloro-4-methyl-1,3-pentadiene, as a fraction boiling within the range 56° -65° C/ 10-11 mm Hg.
• the product was identified by n.m.r. spectroscopy and was shown to be identical with an authentic sample.
• Example 2 The procedure of Example 2 was followed except that the step of distilling off the acetic acid was omitted. This resulted in a slightly higher yield of the product.

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• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Citations (1)

• 1975
  • 1975-04-17 GB GB15862/75A patent/GB1480671A/en not_active Expired
• 1976
  • 1976-04-09 US US05/675,267 patent/US4018838A/en not_active Expired - Lifetime
  • 1976-04-15 DE DE19762616681 patent/DE2616681A1/de not_active Withdrawn
  • 1976-04-16 FR FR7611421A patent/FR2307784A1/fr active Granted
  • 1976-04-16 JP JP51042628A patent/JPS51128902A/ja active Pending

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